1. Field of the Invention
The present invention relates to an optical scanning device implementing a movable mirror as a deflector for scanning an optical beam and a method of manufacturing such an optical scanning device.
2. Description of the Related Art
Conventionally, a polygon mirror or a galvanometer mirror is used in an optical scanning device as a deflector for scanning an optical beam. In order to achieve a high resolution image and high-speed printing, the rotational speed of the deflector needs to be increased. However, in the prior art, high speed scanning technology is restricted by factors such as the durability of the bearing, heat generation due to windage loss, and noise.
In response to such a problem, in recent years and continuing, technology is being developed for applying silicon micromachining to an optical deflector. For example, Japanese Patent No. 2924200 and Japanese Patent No. 3022244 disclose technology pertaining to integrally forming an oscillation mirror and a torsion beam bearing the oscillation mirror on a silicon substrate.
Also, Japanese Patent No. 2924200 discloses a technique for hermetically sealing an oscillation space of an oscillation mirror. According to such a technique, a structure that is processed in depressurized inert gas is hermetically sealed, as is illustrated in FIGS. 1A and 1B.
Also, Japanese Laid-Open Patent Publication No. 8-334722 discloses a technique for hermetically sealing a space with a glass plate through anodic bonding to provide a vacuum space for an electromagnetic power driven oscillation mirror as is illustrated in FIG. 2.
According to the technique of integrally forming an oscillation mirror and a torsion beam bearing the oscillation mirror on a silicon substrate, resonance is used to induce back-and-forth oscillation so that high speed operation may be realized without increasing the noise level. Also, according to this technique, the required drive power for rotating the oscillation mirror is relatively low so that power consumption may be maintained at a low rate.
When an oscillation mirror as is described above is used in an air medium, the following problems arise.
(1) Operational characteristics are influenced by external environmental factors such as temperature, humidity and dust so that reliability is decreased.
(2) A large scanning angle cannot be obtained due to the viscous resistance of air.
Thereby, it is desired that at least the oscillation space of the oscillation mirror be hermetically sealed.
According to the disclosure of Japanese Patent No. 2924200, a single structure is provided on a stem, and a cap is provided over the top portion of the structure to seal the structure. However, complicated processing needs to be conducted using a relatively large number of components including the stem and the cap to realize the above disclosed device structure, and thereby, the manufacturing process for the device structure is quite complicated.
Also, the device structure disclosed in Japanese Laid-Open Patent Publication No. 8-334722 uses an electromagnetic power driven oscillation mirror, and thereby, its manufacturing procedure requires a relatively large number of processes using a relatively large number of components. Also, it is noted that such a device uses a large number of glass plates so that its manufacturing cost may be increased. Further, Japanese Laid-Open Patent Publication No. 8-334722 does not mention mounting the oscillation mirror structure on a printed circuit board with a drive circuit.